Electrophotographic photosensitive member

ABSTRACT

An electrophotographic photosensitive member is composed of a base, a photoconductor layer and an insulating layer laminated in this order, and additionally a rectifying layer is provided between the base and the photoconductor layer.

United States Patent [1 1 Hanada et al.

ELECTROPHOTOGRAPHIC PHOTOSENSITIVE MEMBER inventors: Hiroshi Hanada,Yokohama; Nobuo Kitajima; Tatsuo Masaki, both of Tokyo, all of JapanCanon Kabushiki Kaisha, Tokyo, Japan Filed: June 15, 1971 Appl. No.:153,354

Assignee:

Foreign Application Priority Data June 20, 1970 Japan 45/53956 us. 01.96/1.5, 96/] R, 852/501,

75/134 11, 29/195, 29/197, 29/199, 29/194 1m. (:1 G03g 5/04 Field 61Search 96/1, 15; 252/501 References Cited Primary Examiner-Roland E.Martin, Jr. Attorney-Raymond J. McElhannon et a1.

[5 7 ABSTRACT An electrophotographic photosensitive member is composedof a base, a photoconductor layer and an insulating layer laminated inthis order, and additionally a rectifying layer is provided between thebase and the photoconductor layer.

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ELECTROPHOTOGRAPHIC PI-IOTOSENSITIVE MEMBER BACKGROUND OF THE INVENTIONThis invention relates to an electrophotographic photosensitive member,and more particularly to improvements in an electrophotographicphotosensitive member fundamentally composed of base, photoconductivelayer and insulating layer.

Heretofore, there have been known various inventions ofelectrophotographic photosensitive member of such three layer structure,but most of them are directed to improvement in stable retention ofelectric charge on the photosensitive member. Any useful method forinjecting sufficiently photocarriers has not been disclosed.

SUMMARY OF THE INVENTION The present invention relates to aphotosensitive member comprising a base, a photoconductive layer, aninsulating layer, and a rectifying layer being provided between the baseand the photoconductor layer.

An object of this invention is to provide an improved photosensitivemember comprising three layers.

Another object of this invention is to provide a photosensitive membercapable of retaining stably the charge.

A further object of this invention isto provide a photosensitive memberto which a sufficient photocarrier can be injected.

Still another object of thisinvention is to provide a photosensitivemember'capable of forming an excellent electrostatic image.

A still further object of this invention is to provide a process forproducing these photosensitive members.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates an enlargedcross-section view of an embodiment of electrophotographicphotosensitive member according to the present invention;

FIG. 2 is a graph showing charging characteristics of a photoconductorlayer according to the present invention; 7 I

FIG. 3 is a graph showing charging characteristics of a rectifying layeraccording to the presentinvention;

FIG. 4 is a graph showing charging characteristicsof a photosensitivemember according to the present invention;

FIG. 5 is a graph showing the comparison between the photosensitivemember according to the present invention and the prior art with respectto decay of charge in cases of exposure and dark discharging;

FIG. 6(A) and (B) show charging states of a photoconductor layer and aphotosensitive layer according to this invention, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A representativeelectrophotographic process em ploying a photosensitive member composedof a base,

a photoconductive layer and an insulating layer is a process comprisingprimary charging, secondary charging simultaneously with exposure andblanket irradiation such as electrophotographic processes disclosed inU.S. Ser. No. 563,899, filed July 8, 1966 and U.S. Ser.

No. 571,538, filed Aug. 10, 1966, now abandoned.

According to such electrophotographic processes, electrostatic imagesmay be produced by applying a charge of a certain definite polarity ontothe insulating layer, simultaneously injecting a charge of a polarityopposite to that of the above mentioned charge from the base side so asto bind the charge to the neighbourhood of interface between thephotoconductive layer and the insulating layer and in thephotoconductive layer. And further a DC. voltage corona charging havinga polarity opposite to that of the primary charging or an AC. coronacharging is applied thereto simultaneously with imagewise exposure andthe trapped charge is released at the light portion, but not at the darkportion, and then a blanket irradiation is applied to increase thecontrast and form an electrostatic image.

Important matter in the three layer photosensitive member is pertinentto the charging state of charge trapped by primary charging. It ishighly desired that the charge is stably retained, the sensitivity ofphotoconductor layer is increased and photocarrier is easily andsufficiently injected from the base to thephotosensitive layer.

Referring to FIG. 1, a rectifyinglayer 3 is provided between a highlysensitive photoconductor layer 2 and a base 4 so as to inject easily.photocarriers and retain a charge of a polarity opposite to that of thetrapped charge in an insulating-layer l by primary charging at aneighbourhood of the interface between the photoconductor layer 2 andthe insulating layer.

A photosensitive member having an Se-Te alloy layer provided on aconductor by vapor deposition or plating has sensitivity varyingdepending upon the contents of Te. The more the contents of Te, thehigher the sensi-- tivity. The sensitivity becomes maximum at about 20percent by weight of Te and the resistance decreases, but thecrystallization is accelerated and life of the photosensitive memberitself is shortened.

The present inventors have found that the crystallization can besuppressed without decreasing the sensitivity by incorporating 0.01 to 8percent by weight of Ge, Si or Ge-Se. When the resulting material isused as a photoconductor layer, the Se contains 6 45 percent (by weight)Te and, if desired, additionally contains 0.01 to 8 percent (byweightlGe, Si or Ge-Si. The photoconductor can be vapor-deposited on analuminum plate to form a photoconductor layer. The resultingphotosensitive member is positively or negatively charged by a coronacharger in a dark place for a time of period t. The resulting chargedpotential measured by an electrometer is as shown in FIG. 2. That is,the charge amount at charging time f is decayed gradually by darkdischarging regardless the polarity of the charging. In FIG. 2, adenotes a positive charging curve and b denotes a negative chargingcurve.

On the contrary, when the content of Te in Se is decreased to less thanabout 5 percent, vapor-deposited on an aluminum plate to form aphotosensitive member. Negative and positive charging are applied to thephotosensitive member to give the charging curves as shown in FIG. 3. Ascompared with the curves for large Te content, the surface potential in.case of negative chargingin FIG. 3 is remarkably less. In other words,it is interpreted that injection of positive hole (photocarrier) fromthe conductive layer (base) becomes easy.

When the above-mentioned Se or Se alloys containing various amounts ofTe are used in combination, and positive or negative charging is appliedfor a time of period f, the charging state is as illustrated in FIG. 4.

The negative charging curve is almost the same as that of the rectifyinglayer containing less than 6 percent of Te as shown in FIG. 3 and thepositive charging curve is almost the same as that of photoconductorlayer of relatively high decay as shown in FIG. 2.

FIG. shows a change of surface potential measured by an electrometerwhen a negative charge is applied to a photosensitive member comprisinga photoconductor layer showing the charging and dark dischargingcharacteristics as shown in FIG. 2 and an insulating layer overlyingthereon, and to a photosensitive member comprising a photosensitivelayer having a rectifying property and having the charging and darkdischarging characteristics as shown in FIG. 3 and FlG. 4 and aninsulating layer overlying thereon, for a time of period f anddischarged in a dark place or exposed to light.

In FIG. 5, decay curves for Se or Se alloy containing more than 6percent Te are represented by a and a, where the curve a shows a decaycaused by exposure while the curve a shows a decay caused by darkdischarging. Decay curves for Se or Se alloy containing less than 6percent Te are represented by B and B, where B is for exposure while Bis for dark exposure. There is hardly recognized any difference betweenB and B.

As is indicated in FIG. 5, the surface potential of the photosensitivemember containing Se or Se alloy containing not less than 6% Te(corresponding to the shape of FIG. 2) decreases after charging. Theabovementioned photosensitive member has a distribution of charge whencharged. The charge is injected from the conductive layer 11 as the timepasses to neutralize the charge on the insulating layer 13 and then isdecreased. On the other hand, electrostatic charge is uniformly chargedon the insulating layer 13 and in the neighbourhood of the interfacebetween the insulating layer and the photoconductor layer 12 in case ofproviding a rectifying layer 14 as shown in FIG. (B) and there hardlyappears a decay. This fact indicates that positive I holes aresufficiently injected.

' minum, copper, brass and the like at an optional thickness in adesired form such as sheet, web, plate, drum and cylinder. On the basethere are overlaid a rectifying layer and a photoconductor layer by aknown layer forming method such as a flash method, a co-vapor depositionmethod, a vacuum vapor-deposition method.

The rectifying layer may be formed by vapordepositing on a base achalcogen substance containing 0 6 percent (by weight) Te such As Se,Se-Te, Se Ge, Se-Si, Se-Ge-Si, Se-Te-Ge, Se-Te-Si, Se-Te-Ge-Si and thelike at a temperature of the base of from about 65C to about 80C to formthe deposit layer of about lpt 60p. thick.

The photoconductor layer may be produced by depositing a chalcogensubstance containing more than 6 percent (by weight) Te, preferred withup to 45 percent, such as Se-Te, Se-Te-Ge, Se-Te-Si, Se-Te-Ge-Si and thelike in a thickness of about 1 80;!"

As the insulating layer overlying the photoconductor layer, there may beused any insulating material which is excellent in charge retentionproperty and can pass a radiation to which the photoconductor issensible. Representative insulating materials are organic insulatinglayer such as synthetic resin film, for example, polypropylene andpolyester, inorganic insulating material such as alumina, mica and-thelike, and composite-of inorganic and organic insulating materials.

The following examples are given for illustrating the present invention,but should not be construed as restricting the scope of the invention.

EXAMPLE 1 Se powder (purity of higher than 99.99 percent) and Te powder(purity of higher than 99.99 percent) are mixed in a weight ratio of 9I, placed in a quartz ampoule at about 10 Torr., sealed, and heated atabout 550C for 7 hours to melt the contents. It is preferable tostirring sufficiently the melt by vibration or rotation. The ampoule is,then, put in water to quench. Thus, there is obtained a glassy alloy ofSe-Te. The resulting glassy alloy is vapor-deposited on an aluminum baseto form a photosensitive layer of about 40 thick at 10 10 mm Hg at atemperature of base of 65 C at a temperature of vapor source of about250C. Then, a polyethylene terephthalate film of 25 thick is adhered toa surface of the photosensitive layer by using an epoxy resin to producea photosensitive member of three-layer structure. The resultingphotosensitive member is hereinafter called standard photosensitivemember" On the other hand, Se powder is sealed in a quartz ampoule atabout 10 Torr. The ampoule is heated at about 500C for 6 hours to meltthe contents and the ampoule is, then, put in water to quench. Thus, aglassy selenium is obtained. The glassy selenium is vapordeposited on analuminum base at 10 10 mm Hg at a temperature of base of 65 C at atemperature of vapor source of about 250C to form a rectifying layer ofabout 20 u in thickness. The above mentioned Se-Te glassy alloy isvapor-deposited on the rectifying layer at 10 10 mm Hg at a temperatureof base of 65 C at atemperature of vapor source of about 250C to form aphotosensitive layer of about 30 p. in thick. Then, a polyethyleneterephthalate film of 25 p. in thickness is adhered to the surface ofthe photosensitive layer by using an epoxy resin to form aphotosensitive member of four layer structure.

An electrophotographic method of Japanese Publication No. 24748/1968 isapplied to the standard photosensitive member at an exposure amount of10 lux-sec. to form an image having an electrostatic contrast of about400 V.

On the other hand, when the above-mentioned electrophotographic methodis applied to a photosensitive member according to this invention withthe same conditions as those for the standard photosensitive member, andan electrostatic contrast of as high as about 600 V at an exposureamount of 5 lux-sec. is obtained, and this photosensitive member alsoshows excellent resolving power and panchromatic property. EXAMPLE 2 Se,Te and Ge powders (each being purity higher than 99.99 percent) aremixed in a ratio of atom numher of l 1 l, ball-milled for about 20hours, sealed in a quartz ampoule at about Torr., and heated at about800C for 50 hours to melt the contents. It is preferable to agitate themelt by vibration or rotation. The ampoule is put in water to quench andthus a glassy alloy of Se-Te-Ge is obtained. On the other hand, an alloyof Se-Te alloy (Se Te being 100 7 by weight) is obtained by a proceduresimilar to Example 1. On a surface of Se rectifying layer on an aluminumplate obtained as in Example l there is produced a photosensitive layerof about 30 p. thick by co-vapor deposition method using Se-Te-Ge alloyor Se-Te alloy. The resulting photosensitive layer contains Se, Te andGe in a weight ratio of about 90 l0 0.4. The vapor deposition conditionsare: pressure, 10 4 10' mm Hg; base temperature, 65 82C; vapor sourcetemperature, about 550C for Se-Te-Ge alloy, about 250C for Se-Te alloy.Then, a polyethylene terephthalate film of 25 p. in thickness is adheredto the surface of the photosensitive layer with an epoxy resin toproduce a photosensitive member of four-layer structure.

To the above-mentioned photosensitive member is applied anelectrophotographic process of Japanese Patent Publication No.24748/1968 under the same conditions as in Example 1. There is obtainedan electrostatic contrast of as high as'about 550 V at an exposureamount of 5 lux-sec., and the resolving power, panchromatic property anddurability are also excellent.

We claim:

1. An electrophotographic photosensitive member comprising a base, aphotoconductor layer containing Se-Te, an insulating layer overlying thephotoconductor layer, and rectifying layer means containing selenium andbeing provided between the base and the photoconductor layer forinjecting an electric charge into said photoconductor layer from saidbase, wherein said photoconductor layer contains 6 45% Te and 0.01 8percent of at least one of Ge, Si and Ge-Si.

2. An electrophotographic photosensitive member according to claim 1wherein said rectifying layer means contains Te in an amount up to 6percent by weight.

2. An electrophotographic photosensitive member according to claim 1wherein said rectifying layer means contains Te in an amount up to 6percent by weight.